Paul Callan: While the East Coast was being pounded Thursday by a brutal winter storm, President Donald Trump's latest lawyer, Charles Harder, tossed a "bomb cyclone" of his own into the news cycle.

Harder, who helped put the website Gawker into bankruptcy for its unauthorized publication of a Hulk Hogan sex tape, entered the arena issuing "cease and desist" threats to Michael Wolff, author of "Fire & Fury," the highly unflattering Trump tome, the book's publisher and former Trump chief strategist, Steve Bannon.

Harder previously represented first lady Melania Trump in her defamation lawsuit against the Daily Mail, which resulted in an apology and, according to the Associated Press, a settlement of about $2.9 million.

Harder's threat letter poses a greater risk to Bannon than the truly empty threat of a defamation-related lawsuit naming Wolff and his publishers. The Harder cease and desist letter refers to a "non-disparagement" agreement that was allegedly signed by Bannon during the Trump campaign prohibiting him from "disparaging Mr. Trump, or any of his family members, or any of their businesses, or the campaign." No such agreement would stop Wolff and his publisher from distributing a book quoting Bannon's remarks.

Bannon might quite reasonably assert that such an agreement cannot bind him now as his derogatory references to Trump insiders in the Wolff book focused on the period of the Trump presidency rather than that of the Trump campaign.

After the inauguration, Bannon became a federal employee working as "special counselor to the President" and as such he will claim that he is not bound by an earlier, private sector employment agreement relating to the campaign. He could also assert the First Amendment right of free speech, permitting him to comment on activities that occurred while he worked in the Trump White House.

Any Bannon criticism of the Trump campaign, however, might be fair game for Trump to use in a lawsuit against him, depending on the precise wording of the non-disparagement agreement. Proving damages would be extremely difficult because the President and his family have already been subjected to such an enormous volume of disparaging criticism in the rough and tumble of presidential politics that it would be almost impossible to isolate the impact of Bannon's nasty comments in the Wolff book.

Bannon, therefore, would likely win any lawsuit arising from a campaign non-disparagement agreement signed by him. On the other hand, Bannon might even have a counterclaim against the President, who referred to him as "out of his mind."

Proving a defamation-related lawsuit against Michael Wolff and his publishers would be even more difficult. To win such a case the President must establish that false and defamatory material about the President was published in Wolff's book and that both Wolff and his publishers acted with "actual malice" in publishing the material. This requirement, established in the famous case of New York Times vs. Sullivan, often makes lawsuits filed by public figures impossible to win.

As with the Bannon "disparagement" claim, proof of identifiable damages traceable to Wolff's book would pose yet another insurmountable challenge in a Trump defamation lawsuit. (The publisher is putting the book on sale four days early in light of the anticipated demand for its explosive revelations.)

The President's criminal lawyers will also warn him that any record created in such a defamation trial could be used against the President in criminal or impeachment proceedings. Wolff's attorneys would also be able to take a deposition of the President, possibly asking embarrassing questions related to the inner workings of the White House and about how the President claims his reputation was damaged by the book.

President Bill Clinton's false answer under oath during a deposition in the Paula Jones civil case resulted in one of the charges lodged against Clinton in his impeachment proceedings. Testifying under oath is always risky for a sitting president.

Under these circumstances, the risk to the President would be so great that it is likely that Harder's "cease and desist" letter is no more than the bully bluster used so often by the President in his former life in the real estate industry. But using this tactic from the Oval Office is far more dangerous than from Trump Tower.

Even Hulk Hogan's lawyer can't body slam the fire and fury of Michael Wolff's book -- or Steve Bannon's disdain.

Paul Callan is a CNN legal analyst, a former New York homicide prosecutor and current counsel at the New York law firm of Edelman & Edelman PC, focusing on wrongful conviction and civil rights cases. Follow him on Twitter @paulcallan. The opinions expressed in this commentary are his own.